G.f.: exp( Sum_{n>=1} sigma(n*2^n)*x^n/n ).

Terms

a(0) =1a(1) =3a(2) =12a(3) =47a(4) =157a(5) =531a(6) =1741a(7) =5459a(8) =16814a(9) =51286a(10) =152506a(11) =447622a(12) =1300571a(13) =3721897a(14) =10551143a(15) =29663448a(16) =82494469a(17) =227701487a(18) =624113377a(19) =1697228926a(20) =4586879327a(21) =12323255188a(22) =32904418872a(23) =87395198231a(24) =230972180615a(25) =607363842960